This invention relates to gas-fired, forced-air furnaces and, more particularly, to a fuel efficient, hot combustion gas recirculation system which can be built into new furnaces or installed on existing ones.
Forced-air, gas, home furnaces typically include a combustion chamber where gas is burned to produce hot combustion gases. The hot gases flow through a heat exchanger through which air is circulated so that relatively cool returning air is heated and circulated back through the house. After leaving the heat exchanger, the hot combustion gases are normally vented to the atmosphere through a flue which is connected to a chimney or the like.
By venting hot combustion gases to the atmosphere, a significant amount of heat is allowed to escape unused. Without utilizing this heat, energy is in effect wasted which amounts to greater fuel consumption and larger fuel bills.
Attempts to more effectively utilize this heat by rerouting the hot combustion gases both into the hot air exhausting from the heat exchanger and into the cold air being introduced into the heat exchanger have proved unsatisfactory. Connecting the combustion chamber directly into the heat exchanger exhaust caused the gas burners to blow out, apparently because of the strong air flow generated by the blower. Initial attempts to reroute the hot combustion gases into the cold air return to the heat exchanger caused excessive drafts to flow through the combustion chamber, resulting in the burner being blown out. Although a reduction in the gas flow rate to the burners helped the blowout problem, drafts through the combustion chamber cooled the heat exchanger and lowered the efficiency of the furnace.
A damper installed in the flue pipe which would be closed when the burners were off, during warming of the heat exchanger, and when air is circulating through the heat exchanger caused problems, notably warping of the dampers because of excessive heat and burner blowout due to a buildup of pressure within the combustion chamber when the damper is closed.